Contraceptive action of continuous low doses of norgestrel.

Norgestrel in a dose of 50 mug. was administered daily to 188 women during 2,250 menstrual cycles. Only two pregnancies occurred because of failure of the method, giving a failure rate of 1.1 pregnancies per 100 woman-years. The method was acceptable to most of the subjects, and side-effects, other than menstrual irregularity, were minimal; 68% of the cycles were 28 +/-5 days in length and 21% were less than 23 days. There did not appear to be any increased incidence of amenorrhoea. The antifertility action of continuous administration of low doses of progestogen may be due to an effect on corpus luteum function, in addition to the effects on cervical mucus, endometrium, and tubal transport of ova. The optimum dose of norgestrel appears to be in the range of 50-75 mug./day.